Relation between microstructure, technical properties and neutron radiation shielding efficiency of concrete

Abstract

The paper presents a study on the properties of New Generation Shielding Concrete (NGS-Concrete) modified by materials containing fast neutron moderators and thermal neutron absorbers. The reference ordinary concrete (OC) was modified by the change of the coarse aggregate from crushed granite to magnetite one and cement from CEM III 42.5N to CEM I 42.5R. The addition of gadolinium oxide, polypropylene macro- or/and microfibers, acrylic dispersion, acrylic dispersion together with gadolinium oxide, epoxy dispersion, and finally the inorganic chemical compound containing boron (NaBH4) was used as well. The experimental program included: microstructure studies (analysis of fracture surface, visual and image analysis of cross sections, observations using scanning electron microscopy – SEM, volume and absolute density and total porosity calculated from gravimetric measurements), compressive strength, ultrasonic pulse velocity (UPV) as well as neutron radiation shielding efficiency measurement expressed as half value layer (HVL), determined by the neutron radiation equivalent dose reduction. The relations were investigated using a multiple regression analysis of experimental results. A good correlation between the compressive strength and ultrasonic pulse velocity for all concretes was confirmed. The neutron radiation shielding efficiency expressed as HVL was mainly influenced by volume density (VD). The mathematical model HVL (VD) turned out to be the most reliable, whereas any other independent variable added to this bivariate model was statistically not significant. It was concluded that neutron radiation shielding depends on the volume density of concrete, which is determined mainly by phase and atomic composition changes of aggregate and a lesser extent by microstructure changes.